1. Field of the Invention
The present invention relates to a wireless communication system.
2. Discussion of the Related Art
An IEEE (Institute of Electrical and Electronics Engineers) 802.16m system can support both FDD (Frequency Division Duplex) including H-FDD (Half-Frequency Division Duplex), and TDD (Time Division Duplex).
The IEEE 802.16m system uses OFDMA (Orthogonal Frequency Division Multiplexing Access) as a multiplexing access scheme on downlink (DL) and uplink (UL).
A description will be made of a frame structure of an IEEE 802.16m system that is a mobile communication system.
FIG. 1 illustrates a basic frame structure of the IEEE 802.16m system.
Referring to FIG. 1, one superframe having a size of 20 ms beings with a superframe header (SHF) and is divided into 4 radio frames having a size of 5 ms. When one of channel bandwidths of 5 MHz, 10 MHz and 20 MHz is used, each of the 5 ms radio frames consists of 8 subframes. One subframe can be allocated for DL or UL transmission.
The IEEE 802.16m system, one of mobile communication systems, has more than three types of subframes. Type-1 subframe includes 6 OFDMA symbols, Type-2 subframe includes 7 OFDMA symbols, and Type-3 subframe includes 5 OFDMA symbols.
The basic frame structure can be applied to both FDD including H-FDD, and TDD. In a TDD system, 2 switching points are present in each radio frame. Switching points can be defined according to directivity change from downlink to uplink or from uplink to downlink.
When the channel state between a base station (BS) and a mobile station (MS) is poor in a wireless communication system, a relay station (RS) can be set between the BS and the MS to provide a radio channel in a good state to the MS. Furthermore, an RS can be introduced to a cell boundary area having a poor channel state to provide a high-speed data channel and extend a cell service range. That is, an RS is currently widely used as a technology introduced to remove a radio shadow area in a wireless communication system. While past RSs are limited to repeaters for amplifying a signal and transmitting the amplified signal, recent RSs have been developed into a more intelligent form. Furthermore, RS technology is an essential technology for reducing BS installation cost and backhaul network maintenance cost, extending service coverage, and improving data throughput in next-generation mobile communication systems. With the development of relay technology, RSs used in a conventional wireless communication system need to be supported by a frame structure of a new wireless communication system.
However, no method of configuring frame structures of a BS and RS for supporting the RS in IEEE 802.16m systems has been studied.